Fruit juices, other than fresh squeezed ones, sports drinks and the like are generally prepared by reconstituting or diluting with water a concentrated solution of a flavored sweetener. The quantity of the added sweetener such as cane sugar or the like additive depends on its concentration, wherein a Brix scale value as determined by a saccharometer corresponds to the specific gravity of a saccharide solution. The concentration of saccharides in the prepared sweetened beverage after dilution or reconstitution is comparatively low, suitably for example 5-12 Brix degrees. In the prior art the specific gravity corresponding to the saccharide concentration of an undiluted solution has been relied on for preparation and quality control with another specific gravity corresponding to a target saccharide concentration in the product. A blend ratio by volume is generally calculated in charging a mixing tank with a calculated volume of undiluted solution and water. If an unacceptable error is detected between the actual and target concentrations an appropriate amount of undiluted solution or water is added to the product to adjust its saccharide concentration.
Such a batchwise manner of adjusting the final sweetener concentration, however, is not an efficient way for preparing the product with a target saccharide concentration. This is because the workers have to rely on their senses and their perception when an additional amount of undiluted solution or water has to be added. In a case when an undiluted solution is continuously blended with water for production of a sweet beverage with a target saccharide concentration, the sweetener concentration in the undiluted solution is suitably adjusted at an early stage with a very high precision. The preparation of the undiluted solution requires a great deal of labor and a long time, both impairing productivity.